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Database containers

Overview

You might want to use Testcontainers' database support:

  • Instead of H2 database for DAO unit tests that depend on database features that H2 doesn't emulate. Testcontainers is not as performant as H2, but does give you the benefit of 100% database compatibility (since it runs a real DB inside of a container).
  • Instead of a database running on the local machine or in a VM for DAO unit tests or end-to-end integration tests that need a database to be present. In this context, the benefit of Testcontainers is that the database always starts in a known state, without any contamination between test runs or on developers' local machines.

Note

Of course, it's still important to have as few tests that hit the database as possible, and make good use of mocks for components higher up the stack.

You can obtain a temporary database in one of two ways:

  • JUnit @Rule/@ClassRule: this mode starts a database inside a container before your tests and tears it down afterwards.
  • Using a specially modified JDBC URL: after making a very simple modification to your system's JDBC URL string, Testcontainers will provide a disposable stand-in database that can be used without requiring modification to your application code.

Database container objects

Add a @Rule or @ClassRule to your test class, e.g.:

public class SimpleMySQLTest {
    @Rule
    public MySQLContainer mysql = new MySQLContainer();

Now, in your test code (or a suitable setup method), you can obtain details necessary to connect to this database:

  • mysql.getJdbcUrl() provides a JDBC URL your code can connect to
  • mysql.getUsername() provides the username your code should pass to the driver
  • mysql.getPassword() provides the password your code should pass to the driver

Note that if you use @Rule, you will be given an isolated container for each test method. If you use @ClassRule, you will get on isolated container for all the methods in the test class.

Examples/Tests:

Database containers launched via JDBC URL scheme

As long as you have Testcontainers and the appropriate JDBC driver on your classpath, you can simply modify regular JDBC connection URLs to get a fresh containerized instance of the database each time your application starts up.

N.B:

  • TC needs to be on your application's classpath at runtime for this to work
  • For Spring Boot you need to specify the driver manually spring.datasource.driver-class-name=org.testcontainers.jdbc.ContainerDatabaseDriver

Original URL: jdbc:mysql:5.7.22://somehostname:someport/databasename

Insert tc: after jdbc: as follows. Note that the hostname, port and database name will be ignored; you can leave these as-is or set them to any value.

JDBC URL examples

Using Testcontainers with a fixed version

jdbc:tc:mysql:5.6.23://somehostname:someport/databasename

Using PostgreSQL

jdbc:tc:postgresql:9.6.8://hostname/databasename

Using PostGIS

jdbc:tc:postgis:9.6://hostname/databasename

Using a classpath init script

Testcontainers can run an init script after the database container is started, but before your code is given a connection to it. The script must be on the classpath, and is referenced as follows:

jdbc:tc:mysql:5.7.22://hostname/databasename?TC_INITSCRIPT=somepath/init_mysql.sql

This is useful if you have a fixed script for setting up database schema, etc.

Using an init script from a file

If the init script path is prefixed file:, it will be loaded from a file (relative to the working directory, which will usually be the project root).

jdbc:tc:mysql:5.7.22://hostname/databasename?TC_INITSCRIPT=file:src/main/resources/init_mysql.sql

Using an init function

Instead of running a fixed script for DB setup, it may be useful to call a Java function that you define. This is intended to allow you to trigger database schema migration tools. To do this, add TC_INITFUNCTION to the URL as follows, passing a full path to the class name and method:

jdbc:tc:mysql:5.7.22://hostname/databasename?TC_INITFUNCTION=org.testcontainers.jdbc.JDBCDriverTest::sampleInitFunction

The init function must be a public static method which takes a java.sql.Connection as its only parameter, e.g.

public class JDBCDriverTest {
    public static void sampleInitFunction(Connection connection) throws SQLException {
        // e.g. run schema setup or Flyway/liquibase/etc DB migrations here...
    }
    ...

Running container in daemon mode

By default database container is being stopped as soon as last connection is closed. There are cases when you might need to start container and keep it running till you stop it explicitly or JVM is shutdown. To do this, add TC_DAEMON parameter to the URL as follows:

jdbc:tc:mysql:5.7.22://hostname/databasename?TC_DAEMON=true

With this parameter database container will keep running even when there're no open connections.

Running container with tmpfs options

Container can have tmpfs mounts for storing data in host memory. This is useful if you want to speed up your database tests. Be aware that the data will be lost when the container stops.

To pass this option to the container, add TC_TMPFS paramater to the URL as follows:

jdbc:tc:postgresql:9.6.8://hostname/databasename?TC_TMPFS=/testtmpfs:rw

If you need more than one option, seperate them by comma (e.g. TC_TMPFS=key:value,key1:value1&other_parameters=foo).

For more information about tmpfs mount, see the official Docker documentation.